A bonded piston seal 51 illustrated in FIG. 11 has been conventionally known. The bonded piston seal 51 includes a metal ring 52 and a seal section 53 such as a packing supported by the metal ring 52. The metal ring 52 of the bonded piston seal 51, which is displaced upwardly and downwardly in FIG. 11 by pressure supply, is made to contact to a clutch plate 54, and the clutch plate 54 is pressed by the metal ring 52, so as to engage the clutch.
Further, a plate spring (including a wave spring or a finger spring) 55 for reducing the shock at the time of engaging a clutch (changing speed) is provided between the metal ring 52 and the clutch plate 54 as a separate part, and shocking contact of the metal ring 52 to the clutch plate 54 is cushioned by spring force of the plate spring 55, so as to improve the function for preventing the speed change shock at the time of engaging the clutch.
However, according to the conventional technique, since the plate spring 55 is inserted as a separate part between the metal ring 52 and the clutch plate 54, the number of parts and the assembly manhours are increased, so that there is a problem that the cost is increased.
Patent Document 1: Japanese Patent No. 3515634